Thursday, August 15, 2013

How will crops fare under climate change? Depends on how you ask

Morgan Kelly in Princeton Journal Watch: The damage scientists expect climate change to do to crop yields can differ greatly depending on which type of model was used to make those projections, according to research based at Princeton University. The problem is that the most dire scenarios can loom large in the minds of the public and policymakers, yet neither audience is usually aware of how the model itself influenced the outcome, the researchers said.

The report in the journal Global Change Biology is one of the first to compare the agricultural projections generated by empirical models — which rely largely on field observations — to those by mechanistic models, which draw on an understanding of how crop growth and development are affected by the environment. Building on similar studies from ecology, the researchers found yet more evidence that empirical models may show greater losses as a result of climate change, while mechanistic models may be overly optimistic.

The researchers ran an empirical and a mechanistic model to see how maize and wheat crops in South Africa — the world’s ninth largest maize producer, and sub-Saharan Africa’s second largest source of wheat — would fare under climate change in the years 2046 to 2065. Under the hotter, wetter conditions projected by the climate scenarios they used, the empirical model estimated that maize production could drop by 3.6 percent, while wheat output could increase by 6.2 percent. Meanwhile, the mechanistic model calculated that maize and wheat yields might go up by 6.5 and 15.2 percent, respectively.

In addition, the empirical model estimated that suitable land for growing wheat would drop by 10 percent, while the mechanistic model found that it would expand by 9 percent. The empirical model projected a 48 percent expansion in wheat-growing areas, but the mechanistic reported only 20 percent growth. In regions where the two models overlapped, the empirical model showed declining yields while the mechanistic model showed increases. These wheat models were less accurate, but still indicative of the vastly different estimates empirical and mechanistic can produce, the researchers wrote.

…“A yield projection based only on empirical models is likely to show larger yield losses than one made only with mechanistic models. Neither should be considered more right or wrong, but people should be aware of these differences,” Estes said. “People who are interested in climate-change science should be aware of all the sources of uncertainty inherent in projections, and should be aware that scenarios based on a single model — or single class of models — are not accounting for one of the major sources of uncertainty.”…

June 2009 – At the studios of Cleanskies TV, I was interviewed about the costs of climate change, and discussed adaptation efforts underway in the US and around the world.

May 2009 – I helped draft the scenarios for Rising Waters, a multistakeholder scenarios effort focused on climate change adaptation in the Hudson Valley. The final report is now completed and available here.

May 2008 – I reviewed two books on climate and energy in the New Leader magazine: James Gustave Speth's The Bridge at the Edge of the World: Capitalism, the Environment and Crossing from Crisis to Sustainability, plus Robert Bryce's Gusher of Lies: The Dangerous Delusions of Energy Independence.

January 2008 – A very local paper covers a very global issue.... The Litchfield County Times in northwestern Connectictut ran an article in January 2008 about Carbon-Based.

Now available: Climate Change Adaptation in 2011

A selection of my writings from 2011, plus some of my posts, as well as links... all focusing on the risks of climate change